Chapter 3 Summary: Bio Textbook

Chapter 3-1: What is Ecology?

Ecology is the study of the interactions between organisms and other organisms and the interaction between organisms and their environment. The study of ecology focuses on the different ways in which life on Earth is organized, from the smallest cell to the entire planet (or biosphere). The interactions that take place within the biosphere have over the eons woven a web of interdependence; put simply, each organism on Earth, in some way is connected with every other organism on Earth. This is why the extinction of even one species has such a devastating effect on wildlife all around the world. Due to the fact that life on Earth is constantly evolving, adapting and changing, the biosphere is far from static, and it is one of the most dynamic subjects in science.

One key aspect of ecology is “levels of organization”. This term refers to the different levels of complexity that an ecologist may study. The ecologist may study a single individual animal, or the entire biosphere. As the complexity increases, different factors are taken into account, such as the environment and the other species present in the area. Obviously, the most complex level is the biosphere itself. The levels are as follows:

• ·      Individual: an individual organism, which can be a plant, animal, or microorganism.
• ·      Species: A group of that same animal, plant or microorganism, similar enough that they can breed and produce fertile offspring.
• ·      Population: A group of the same species, residing in the same general area.
• ·      Community: Multiple populations and species residing in the same general area and forming a food chain.
• ·      Ecosystem: A collection of all the organisms that live in a particular place, as well as their physical environment, and external factors such as weather.
• ·      Biome: A group of ecosystems that have the same general climate conditions and the same dominant communities.

• ·      Biosphere: The entire planet.

Ecologists use many methods and tools to study the living  (and nonliving) world. For those that study the bigger organisms, binoculars, field guides and radio tracking tags might be their tools of the trade. The ecologists that study the microscopic world may do so with microscopes and Petri dishes. Despite the differences in tools or methods, all ecologists use three basic scientific approaches: observing, experimenting and modeling.

•       Observing: Observations are usually questions that ecologists ask, and form the first step towards ecological study. Some of these questions are simple, such as “How many species live here”? Others are more complex, such as “Why is one community more susceptible to climate change than another”? Observations are the first step to designing experiments and models.
•        Experimenting: This is fairly self-explanatory; it involves an ecologist designing and setting up an experiment to test out hypotheses. Ecologists can perform experiments in artificially created environments or conduct them within the natural world.
•      Modeling: Many ecological phenomena occur over such a large period of time or across so vast a distance that it would be highly impractical and difficult to study. Therefore, models are made to study the effects of ecological phenomena on the natural world, such as the effect of global warming on an ecosystem. With the advent of complex simulation programs and powerful supercomputers, ecologists have been able to make more complex and more accurate models. However, such predictions are still (to the best of the ecologist’s ability) confirmed by experiments and observations.

Chapter 3-2: Energy Flow

Every organism in the world needs energy to power the complex chemical reactions that take place within its body. Where does the energy that allows ants to carry objects many times their size or the energy that allows birds to migrate thousands of miles come from? The flow of energy through an ecosystem is a key factor in determining the system’s ability and capacity to sustain life.

The main source of energy for life on Earth is sunlight. Without this precious resource, an organism cannot function. Interestingly, only 1% of all the sunlight that hits the Earth is used by living organisms, but this is enough to produce as much as 3.5 kilograms of living tissue per square meter a year in some tropical forests. The reasoning behind the fact that many religions worship the sun as the giver of life is not hard to understand. Most ecosystems are divided into 3 classes, the producers, the consumers, and the decomposers. In most cases, the producers will be plants. Producers are autotrophs, that is, organisms that can produce their own food within their bodies. Plants do this via photosynthesis. Most organisms, like herbivores, carnivores and decomposers depend on energy stored in inorganic molecules. Usually, this comes in the form of glucose, which plants synthesize through photosynthesis. When herbivores eat plants, in receives the glucose within the plant, and the energy within the glucose. Carnivores eat the herbivores, thereby receiving a portion of that energy. Lastly, the decomposers break down organic molecules and deceased organisms. In this way, energy is recycled and continually replenished in a never-ending cycle. The theme of predators eating prey, that themselves eat plants is also referred to as the food chain.

However, nothing in nature is ever so linear and streamlined as a simple food chain. Many consumers are omnivores, eating both plants and animals. Others are detritivores that eat organic detritus produced by decomposers. When people try to illustrate this using something as simple as a food chain things start getting very complex. To help them better understand the feeding relationships within an ecosystem ecologists produce food webs. Put simply, food webs show what eats what in a given ecosystem. They also display what level each organism is at, from producers to third-level consumers. These are called trophic levels. Since only 10% of the energy from one trophic level makes it to the next, each trophic level can only support 10% of the organisms. This is why there are usually only 1 or 2 apex predators at the top of the food chain; that is all that the apex trophic level can support.

Chapter 3-3: Cycles of Matter

In most organisms, more than 95% of the body is made up of just four elements: oxygen, hydrogen, carbon, and nitrogen. Fortunately, these elements are readily available on Earth, but the cell of living creatures cannot use them unless they are in some suitable form. Energy and matter move through ecosystems in different ways. Energy flow is a one-way cycle, while matter is constantly recycled within the system. Matter passes from one part of the biosphere in the form of biogeochemical cycles. As the word suggests, matter is transformed from organic to inorganic many times throughout its journey. The word transformation is key: Systems never actually use up matter completely; they just transform it from one form into another. In keeping with the law of conservation of mass and energy, no matter or energy is ever created or destroyed; it is only transformed. This means that there will always bee a fixed amount of matter and energy cycling through an ecosystem. There are many different types of cycles (of matter) that take place within the natural world. The most important ones are the water cycle, the nutrient cycle, the carbon cycle, and the nitrogen cycle.

The water cycle is the simplest. The heat of the sun evaporates water. This water, which was once part of the ocean, forms into clouds. Water can also evaporate from the leaves of plants. This is called transpiration. The clouds will then condense into liquid water, which is then released in the form of precipitation. Precipitation is not just rain; it can be snow, hail or sleet. When precipitation hits the ground, much of it runs off into rivers, lakes and streams, which carry the water back to the sea. Some water seeps into the soil, going as far down as to become groundwater. Water in soil enters plants through roots, and the water cycle begins anew. Scientists estimate that it may take a single molecule of water 4000 years to complete the water cycle. This means that the water in a reservoir could have been there for hundreds of years. Similarly, the clouds we see in the sky are probably ancient.

The nutrient cycle is the path that various nutrients take in their journey through a system. Nutrients are the chemical building blocks of your body, and carry out the essential life functions and chemical reactions that allow an organism to live. Without nutrients, an organism cannot function. Primary producers usually obtain their nutrients in simple inorganic forms from the surrounding environment. First level consumers gain their nutrients by eating the plants; second level consumers gain their nutrients by eating first level consumers, and so on.

The carbon cycle is especially important, as the life forms we know of are all carbon based.  Carbon is a key ingredient in living tissue, and can take many forms, all of which are used in the natural world.  Calcium carbonate is a key component of animal skeletons. Carbon dioxide is a major part of the atmosphere. Plants also use carbon dioxide during photosynthesis. There are four main types of processes that move carbon through its cycle.

• ·      Biological processes, such as photosynthesis, respiration and decomposition take up and release carbon and oxygen.
• ·      Geochemical processes, such as erosion and volcanic activity, release carbon dioxide into the atmosphere and oceans.
• ·      Mixed biogeochemical processes, such and the decomposition of buried organisms into coal and fossil fuel stores carbon underground
• ·      Human impact, such as mining, cutting and burning forests, and burning fossil fuels, release carbon dioxide into the atmosphere.

The nitrogen cycle is important because all organisms require nitrogen to make amino acids, the building blocks of proteins. Human activity adds nitrogen to the biosphere in the form of nitrate, a major component of chemical fertilizers. Nitrogen gas is the most common form of nitrogen on Earth, but only a small percentage of bacteria can use it in this form. These bacteria convert nitrogen to ammonia through a process called “nitrogen fixing”. Ammonia is a form of nitrogen that many organisms can readily use; therefore the nitrogen cycle is dependent on these bacteria. When organisms die, they are broken down by decomposers and return nitrogen to the soil in the form of ammonia.  Some bacteria convert nitrates into nitrogen gas via a process called denitrification. This replenishes atmospheric nitrogen and allows to cycle to begin again.